corpus luteum

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A yellow, progesterone-secreting mass of cells that forms from an ovarian follicle after the release of a mature egg.

Wiktionary

1. n. anatomy A yellow mass of cells that forms from an ovarian follicle during the luteal phase of the menstrual cycle in mammals; it secretes steroid hormones.

GNU Webster's 1913

1. n. (Anat.) the reddish yellow mass which fills a ruptured Graafian follicle in the mammalian ovary.

WordNet 3.0

1. n. yellow endocrine tissue that forms in a ruptured Graafian follicle following the release of an ovum; it degenerates after a few days unless pregnancy has begun